JPH0239142B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an error recovery method by retransmission when a data transmission error occurs in a data communication network in which data is transmitted via a relay station using a wireless communication circuit.

As a data transmission control procedure, for example, ISO
There is an HDLC (High Level Data Link Control) procedure that has been standardized by the International Organization for Standardization (International Organization for Standardization). this
The HDLC procedure is a transmission control procedure established for the purpose of efficiently performing high-speed data transfer.
Since this procedure is expected to become widespread in the future, the description of this invention will be based on the HDLC procedure. Furthermore, since the HDLC procedure is already known, the HDLC procedure is
A general description of the procedure will be omitted.

FIG. 1 is a format diagram showing the basic structure of an HDCL frame.The control unit contains a frame transmission number and a reception frame number, and continuous frame transfer is possible by managing these numbers. Also
The FCS (Frame Check Sequence) can check all transmitted bits for transmission errors, and as a result of this check, if a transmission error exists, the transmission number of the control unit frame is continuously detected. If the number is missing, it is determined that the frame has not arrived at all (that is, the frame is lost), and retransmission control is performed.

Figure 2 is a format diagram showing the format of the control unit. Frames are classified into information transfer frames, monitoring frames, and unnumbered frames depending on their purpose, and the 8 bits of control unit bit numbers 1 to 8 indicate the type of frame. Therefore, it is used as shown in Figure 2, where 0 and 1 represent fixed bit logics ``0'' and ``1'', respectively, N(S) is the transmission sequence number, and N(R) is the reception sequence number. , all of them can give 8 types of numbers using 3 bits, P/F is a poll/final bit, and when the poll bit is logic ``1'', it means soliciting a response from the other station; The bit is set to logic "1" and sent when transmitting a response frame to a command frame in which the poll bit is logic "1". Paul bit "1"
A station that receives a command frame must transmit a response frame with a final bit of "1" as soon as possible. S is a monitoring function bit, which identifies the type of monitoring frame.
M is a modification function bit that identifies the type of non-numbered frame.

In the HDLC procedure, there are four types of retransmission procedures: (1) retransmission by poll/final bit, (2) retransmission by REJ (Reject), (3) retransmission by SREJ (Selective Reject), and (4) retransmission by timeout. However, since the method of the present invention described below can be applied to any of the retransmission methods described above, the following description will be made using the case of retransmission by REJ (Reject) as an example.

Each time the receiving station receives an information transfer frame, it checks N(S) (transmission sequence number) in the control unit, and if there is a missing number in N(S), it means that the information transfer frame is missing. The N(S) of the information transfer frame currently in use is notified to the other station using a monitoring frame. The type of monitoring frame used at this time is the previously mentioned REJ (Reject), and the missing N(S) is inserted into N(R) of the control unit to request retransmission. The station that received the REJ retransmits all frames after the lost information transfer frame.

Figure 3 is an operation time diagram showing the state of retransmission due to a retransmission request, where station 1 is a transmitting station, station 2 is a receiving station, and I _a,b
(In the example in Figure 3, a is 0, 1, 2, 3, 4... and b
=0) is the information transfer frame, a is the value of N(S),
b is the numerical value of N(R), and the symbol 〓 means a transmission error. When station 2 receives I ₁ , ₀ and then receives I ₃ , ₀ , it knows that I ₂ , ₀ is missing and sends REJ, 2.
After receiving this, station 1 retransmits I ₂ , ₀ , I ₃ , ₀ , I ₄ , ₀ after transmitting I ₄ , ₀ .

By the way, when a line with a large propagation delay time, such as a satellite line, is used as a transmission path, retransmission using REJ has the disadvantage that error recovery time becomes long and line utilization efficiency decreases. FIG. 4 is a diagram showing an example of a retransmission sequence according to the conventional method. The same symbols and symbols as in FIG. 3 have the same meanings, and station 2 detects an N(S) order error at time _t REJ, 2 is sent, and this reaches station 1 at time t ₁ , and station 1 starts retransmitting I ₂ , ₀ , but before that, it has already
I ₃ , ₀ to I _o,0 are being sent. Even if station 2 receives this, it will not receive the I ₂ , ₀ frame requested by REJ, 2 until the N(S) order is restored to normal, that is, from time t ₀ to time t ₂ in Figure 4. The frame is rejected as invalid.

Conventional retransmission is performed as described above,
If we define the time it takes for radio waves to travel back and forth between the earth and the satellite as one round trip time, at least two round trip times are required for error recovery, and the frames sent during this time are The drawback was that it was sent in vain.

This invention was made in order to eliminate the drawbacks of the conventional systems as described above. Frames transmitted by the own station relayed by the satellite can also be received by the own station, so the frame transmitted by the own station can be monitored by this reception. By combining the conventional retransmission procedure with the procedure of voluntarily retransmitting the data if deemed necessary,
The purpose is to quickly recover from errors and improve line usage efficiency.

Embodiments of the invention will be described below with reference to the drawings. FIG. 5 is a sequence diagram showing an embodiment of the present invention. The same characters and symbols as in FIG. Because we are monitoring (in the diagram)
Shown with Echo Back. The same applies hereafter), the lack of I _2,0 is detected at time t ₃ , and _it is spontaneously retransmitted from station 2 in the same procedure as when REJ, 2 was received, and this reaches station 2 at time t ₄ . REJ, 2 transmission from station 2 at time t ₀ , REJ retransmission from station 1 at time t ₁ , and arrival at station ₂ at time t 2 are the same as in the case of FIG. Therefore, the error recovery time T
In the case of FIG. 4, there are two round trips between t ₀ and _{t 2} , but in the case of FIG. ₅ , there is one round trip between t ₀ and t 4. In the case of , the frame arrives at station 2 between t _{0 and t 2} , but in the case of Fig. 5, the frame arrives at station 2 between t ₀ and t ₄ and between t ₄ and _{t 2} . In the case of FIG. 5, N does not increase more than in the case of FIG.

In the example shown in Figure 5, station ₂
Since I ₃ , ₀ to _{I l,0} are received, all relevant frames are discarded by N(S) order error detection, but the transmission timing of frames after I ₃ , ₀ at station 1 is t ₃ After this point, unnecessary frame discards will not occur at all. In the case of Figure 4, at least
I ₃ , ₀ is rejected once. Also, in the example in Figure 5,
Regardless of whether I ₂ , ₀ to _{I n,0} received between t ₄ and t ₂ at station 2 are correctly received frames,
At time t ₂ , double reception is discovered and rejected, but this procedure is an existing procedure in HDLC. Even if REJ,2 sent from station 2 does not reach station 1 correctly at time t ₀ , there will be no problem according to the method of the present invention, and instead frames from I ₃ , ₀ to _{I n,0} However, in the conventional method (FIG. 4), if REJ,2 does not reach station 1 correctly, it becomes necessary to retransmit the REJ frame, further reducing transmission efficiency.

FIG. 6 is a sequence diagram showing another method similar to the present invention, in which the same characters and symbols as in FIG. In this example, the missing frame I ₂ , ₀ is detected at time t ₃ and only frame I ₂ , ₀ is retransmitted, followed by sending frame I ₅ , ₀ at t ₅ . It is. In this way, the error recovery time is shortened as in the case of Fig. 5, but
N(S) order error detection occurs twice, and the transmission efficiency is even lower than that of the conventional method.

When applying this invention to the SREJ method,
Since the station that receives SREJ retransmits only the lost information transfer frame, it seems that the effect of this invention cannot be expected, but even in this case, if there are two or more transmission errors within two round trip times, is effective.

Figure 7 shows the SREJ retransmission sequence according to the conventional method, and Figure 8 shows the SREJ retransmission sequence according to the present invention. In these drawings, the same characters and symbols as in Figure 6 have the same or similar meanings. . According to the HDLC procedure regulations, only one SREJ abnormal state is allowed for each direction of information transfer, that is, the SREJ cannot output the next SREJ until the corresponding retransmission frame is received. In the case of Fig. 7, station 2 recognizes the omission of I ₁ , ₀ at t ₀ and the omission of I ₃ , ₀ at t ₆ , and sends SREJ, 1 at t ₀ .
It reaches station 1 at time t ₁ , and station 1 retransmits I ₁ , _0. This reaches station 2 at time t ₂ , and station 2 sends SREJ, 3. At t ₇ , station 1 retransmits I ₃ , 0. ₀ is retransmitted and reaches station 2 at time _t8 . In the case of Fig. 8, t ₃ at station 1
At time _t9 , an error in _I1F0 is detected, and at time _t9 , an error in _I3 , ₀ is detected, and _I1 , ₀ , _I3 , ₀ are retransmitted, respectively, and station 2
Since the missing I _{1 , 0} is detected at time t 0, and the missing I ₃ , ₀ is detected at t ₁₀ , and SREJ, 1 and SREJ, 3 are sent respectively, comparing Figures 7 and 8 reveals that there is no error. In the case of FIG. 7, the recovery time T is 2 round trip times + N(S) sequence error detection waiting time + SREJ transmission waiting time, whereas in the case of FIG. 8 it is 1 round trip time. In addition, the number of rejected frames N is twice that in the case of Fig. 7, as shown in Fig. 8, but since SREJ is originally used only when the value of N in Fig. 7 is small, this number is doubled. This is not a huge disadvantage.

In the above explanation, when transmitting station 1 transmits frames from its own station that are relayed by satellite and broadcast toward the earth (referred to as downlink), the propagation conditions for stations 1 and 2 are considered to be similar. We decided to resend it. However, in reality, the downlink status may differ between station 1 and station 2 due to the influence of regional rainfall. Figure 9 shows that when there is a failure only for station 2 on the downlink,
Figure 10 shows the sequence of SREJ retransmission according to the present invention when there is a failure only for station 1 on the downlink, the case in Figure 9 is similar to the conventional SREJ retransmission, and the case in Figure This method only causes unnecessary retransmission, and there is no problem overall as an information transfer method.

Further, in the case of retransmission by poll/final bit or retransmission due to timeout, the method of the present invention has the same effect as in the case of retransmission by REJ.

In the above embodiment, explanation was given assuming a time division multiple access communication system, but even in the case of a frequency division system, a transmitting station receives frames transmitted from its own station that are relayed by a relay station and sent out. The present invention can be similarly applied as long as it is in a state where it can be monitored.

Although the HDLC procedure is assumed as the transmission control procedure, the method of the present invention can also be applied to other transmission control procedures (for example, the BASIC procedure) to produce effects as long as they have a retransmission procedure.

When data is transmitted wirelessly as described above, if the present invention is used in combination with retransmission control at the transmitting station, error recovery time can be significantly shortened and transmission efficiency can be improved.

[Brief explanation of drawings]

Fig. 1 is a format diagram showing the basic configuration of an HDLC frame, Fig. 2 is a format diagram showing the format of the control section shown in Fig. 1, Fig. 3 is an operation time diagram showing the state of retransmission due to a retransmission request, and Fig. 4 is a format diagram showing the format of the control section shown in Fig. 1. FIG. 5 is a sequence diagram showing a conventional method, FIG. 5 is a sequence diagram showing an embodiment of the present invention, and FIG. 6 is a sequence diagram showing another method similar to the present invention.
Fig. 7 is a sequence diagram showing the conventional method of SREJ, Fig. 8 is a sequence diagram showing the method of the present invention in SREJ, Fig. 9 is a sequence diagram showing the case of downlink accident for only station 2,
FIG. 0 is a sequence diagram showing the case of a downlink failure for only station 1. Note that the same characters and symbols in the figures have the same or similar meanings.

Claims (1)

[Claims] 1. In a retransmission control method in which data is retransmitted at the request of a receiving station when data is transmitted via a relay station installed on an artificial satellite using a wireless communication line,
A stage in which a transmitting station that transmits data receives and monitors the data sent by itself being relayed by a relay station, and when a condition requiring retransmission of the data is detected in this stage, the receiving station 1. A retransmission control method comprising the step of voluntarily retransmitting the data using the same procedure as the procedure of retransmitting the data upon request.